The stainless steels that are used in firearms can be heat treated, but you have to know WHAT the steel is, and what procedures are needed to bring it to what level of hardness, and for what purpose.

For the most part, a gun with stainless steel parts has already been heat treated to the ideal level by the manufacturer.
Attempting to heat treat it to another standard will likely cause serious problems.
Gun parts are treated to a certain level for the purpose the part is to be used for.
Making it harder or softer will usually cause broken parts, or unsafe parts.

In other words, a gun maker doesn't "save money" by not hardening a part to a higher level. The part is hardened to the ideal level.....no harder...no softer, as determined by well educated firearms engineers who fully understand the stresses involved.

Bottom line, you're not going to outguess engineers and metallurgists with masters degrees.

As Dfariswheel said, do not try to heat treat firearms parts yourself. Also, realize that there is a very distinct relationship between hardness and strength (any kind of strength: yield, shear, tensile, etc) for any metal. Making a metal piece harder may actually make it break easier. Just trust that the manufacturers know more about what they are doing than you do.

Thanks guys, that's what I figured. Just getting desperate in restoring an AMT .45DAO back up gun. I know they have had a lot of production problems as well as operational ones. I was actually doing well with it, and even customized modern mags to overcome the feed issues. Then, the barrel lug cracked and opened up about 1/8". A welder is repairing it but it will wind up in my spare parts bin. I have another barrel on the way thanks to this forum, but don't want the same thing to happen.

The stainless steels that are used in firearms can be heat treated, but you have to know WHAT the steel is, and what procedures are needed to bring it to what level of hardness, and for what purpose.

"Eggs-zackly". Most/many people do not realize that "stainless steel" is not one alloy but many different(way more than thirty), under three general classifications, Ferritic, Austinetic, and Martinsitic. Martinsitic stainless steels can be hardened in common quenching means (oil and water). However Austenetic steels usually employ a sub-zero quench (liquid Nitrogen?), to achieve full hardness. You gots to know what it is and what to do with it.
One of the most frequent misconceptions is that, "...stainless steel, is non-magnetic..." Some are...some are not. Take out your 440-C stainless steel pocket knife and test it with a magnet and see what happens.
So, to the question: "Can Stainless Steel pistol parts be heat treated to gain additional strength?" The answer would be: Probably, but not by someone other than those with the proper knowledge and skills.

__________________Sometimes you get what you pay for, sometimes you only pay more for what you get.
Three shots are not a "group"...they are a "few".
If the Bible is the literal, infallible, unerring word of God...where are all those witches I am supposed to kill? (Exodus 22:18)

Austenitic stainless is rarely quenched.
Sub-zero quench is - 100 F, Cryogenic quench is - 300 F [ LN ].
The number of stainless steels used in firearms is long ! Each is chosen for a particular job and heat treated for that job. Toughness is is usually an important consideration.
Heat treating and welding unknown steels can be a dangerous practice !!!

I some special applications it is...Kershaw knives used to advertise: "... high carbon AUS series stainless steel, using an advanced sub-zero quench ...", in some of their knife blades. Which always peaked my curiosity inasmuch as AUS (Austinetic) stainless-es, to the best of my knowledge are low carbon.

__________________Sometimes you get what you pay for, sometimes you only pay more for what you get.
Three shots are not a "group"...they are a "few".
If the Bible is the literal, infallible, unerring word of God...where are all those witches I am supposed to kill? (Exodus 22:18)

The one I know that was heat treated, was some of the 400 series, due to the amount of iron, and carbon in it. However, the 400 series can show a rust too. They use this in pump parts, and I remember machining some of them, especially sleeves. They got these hard as H##l, and the tool would practically bend, while turning the part in a lathe, when it was time for the finishing after heat treating. Really, they should have been ground with a tool post grinder.

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